Pedicle screw assembly and methods therefor

ABSTRACT

A method for stabilizing a spine includes providing a coupling element having upper and lower ends, a rod receiving opening adapted to receive an elongated stabilizing rod, a bore extending through the lower end and a conical-shaped seat surrounding the bore adjacent the lower end; providing a fastener having upper and lower ends, a head having a radial surface, and at least one anchoring element between the lower end of the fastener and the head; assembling the fastener with the coupling element so that the lower end of the fastener passes through the bore of the coupling element and the radial surface of the head engages the conical-shaped seat. The method also includes anchoring the fastener to bone; moving the coupling element relative to the fastener for capturing the elongated stabilizing rod in the rod receiving opening; and urging the captured stabilizing rod toward the head of the fastener so that the rod contacts the head and forces the radial surface of the head against the conical-shaped seat of the coupling element for locking the coupling element from further movement relative to the fastener.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/755,846 filed Jan. 5, 2001.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to spinal fixationdevices and more specifically relates to a pedicle screw assembly havinga low profile and having an improved screwhead/coupling elementinterface for locking the assembly.

[0003] The spinal column is a highly complex system of bones andconnective tissues that provides support for the body and protects thedelicate spinal cord and nerves. The spinal column includes a series ofvertebrae stacked one atop the other, each vertebral body including aninner or central portion of relatively weak cancellous bone and an outerportion of relatively strong cortical bone. Situated between eachvertebral body is an intervertebral disc that cushions and dampenscompressive forces experienced by to the spinal column. A vertebralcanal containing the spinal cord and nerves is located behind thevertebral bodies.

[0004] There are many types of spinal column disorders includingscoliosis (abnormal lateral curvature of the spine), kyphosis (abnormalforward curvature of the spine, usually in the thoracic spine), excesslordosis (abnormal backward curvature of the spine, usually in thelumbar spine), spondylolisthesis (forward displacement of one vertebraover another, usually in a lumbar or cervical spine) and other disorderscaused by abnormalities, disease or trauma, such as ruptured or slippeddiscs, degenerative disc disease, fractured vertebra, and the like.Patients that suffer from such conditions usually experience extreme anddebilitating pain, as well as diminished nerve function.

[0005] The present invention generally involves a technique commonlyreferred to as spinal fixation whereby surgical implants are used forfusing together and/or mechanically immobilizing vertebrae of the spine.Spinal fixation may also be used to alter the alignment of adjacentvertebrae relative to one another so as to change the overall alignmentof the spine. Such techniques have been used effectively to treat theabove-described conditions and, in most cases, to relieve pain sufferedby the patient. However, as will be set forth in more detail below,there are some disadvantages associated with current fixation devices.

[0006] One spinal fixation technique involves immobilizing the spine byusing orthopedic rods, commonly referred to as spine rods, that rungenerally parallel to the spine. This may be accomplished by exposingthe spine posteriorly and fastening bone screws to the pedicles of theappropriate vertebrae. The pedicle screws are generally placed two pervertebra and serve as anchor points for the spine rods. Clampingelements adapted for receiving a spine rod therethrough are then used tojoin the spine rods to the screws. The aligning influence of the rodsforces the spine to conform to a more desirable shape. In certaininstances, the spine rods may be bent to achieve the desired curvatureof the spinal column.

[0007] U.S. Pat. No. 5,129,388 to Vignaud et al. discloses a spinalfixation device including a pedicle screw having a U-shaped head rigidlyconnected to an upper end of the screw. The U-shaped head includes twoarms forming a U-shaped channel for receiving a spine rod therein. TheU-shaped head is internally threaded so that a set screw having externalthreads may be screwed therein. After the pedicle screw has beeninserted into bone and a spine rod positioned in the U-shaped channel,the set screw is threaded into the internal threads of the U-shapedchannel for securing the spine rod in the channel and blocking relativemovement between the spine rod and the pedicle screw. The fixationdevice also includes a cap covering an upper portion of the U-shapedhead to prevent the arms from spreading upon threading the set screwinto the internal threads of U-shaped head.

[0008] Surgeons have encountered considerable difficulty when attemptingto insert spinal fixation devices such as those disclosed in theabove-mentioned '388 patent. This is because the U-shaped heads ofadjacent screws are often out of alignment with one another due tocurvature in spines and the different orientations of the pediclesreceiving the screws. As a result, spine rods must often be bent inmultiple planes in order to pass the rods through adjacent U-shapedchannels. These problems weaken the strength of the assembly and resultin significantly longer operations, thereby increasing the likelihood ofcomplications associated with surgery.

[0009] In response to the above-noted problems, U.S. Pat. No. 5,733,286to Errico et al., U.S. Pat. No. 5,672,176 to Biedermann et al., and U.S.Pat. No. 5,476,464 to Metz-Stavenhagen disclose polyaxial spinalfixation devices wherein the anchoring element fixed to the bone has aspherically-shaped head. The fixation devices in the above-identifiedpatents also have orthopedic rod capturing assemblies for securingorthopedic rods in the capturing assemblies and connecting the rods withthe anchoring elements. The spherically shaped heads of the anchoringelements permit movement of the anchoring elements relative to theorthopedic rod capturing assemblies. However, the above-mentionedpatents do not solve all of the deficiencies of fixation devices such asthose described in the Vignaud '388 patent because the respective spinalfixation devices may shift following insertion. This is due primarily tothe fact that there is insufficient surface area contact between thespherically-shaped heads of the anchoring elements and the rod capturingassemblies. In addition, the devices are complex, include many parts,and are difficult to manufacture.

[0010] In certain preferred embodiments of commonly assigned U.S. patentapplication Ser. No. 09/414,272, filed Oct. 7, 1999, the disclosure ofwhich is hereby incorporated by reference as if fully set forth herein,a pedicle screw assembly includes a fastener having a tip end forinsertion into bone and an expandable head at the opposite end of thefastener. The expandable head has an outer surface including a convexportion, a recess having an inner surface and defining an innerdimension, and at least one slot extending between the inner and outersurfaces thereof for allowing expansion of the head. The assembly alsohas an insert which can be positioned at least partially in the recess,the insert having an outer surface and defining an outer dimension thatis greater than the inner dimension of the recess. The assembly includesa coupling element having a rod receiving opening, a bore for receivingthe fastener, and a seat for receiving the head of the fastener, theseat including a concave portion for receiving the convex underside ofthe head and allowing the fastener to pivot and rotate relative to thecoupling element before being locked therein. After an orthopedic rodhas been positioned within the coupling element, a locking elementassociated with the coupling element locks the orthopedic rod in therod-receiving opening. The locking element is adapted to be forcedagainst an orthopedic rod arranged in the rod receiving opening, to inturn force the insert into the recess of the expandable head so that theouter dimension of the insert bears against the inner dimension of thehead, thereby expanding the outer surface of the head against theconcave seat of the coupling element for locking the fastener fromfurther pivotal movement relative to the coupling element. In otherpreferred embodiments, the head is expandable by virtue of the materialof which it is made such as carbon fiber.

[0011] In spite of the above-mentioned devices, there remains room forimprovement of prior art spinal fixation devices in the manner oflocking the screwhead, the complexity of use, difficulty in properlypositioning the orthopedic rod and the rod-capturing assemblies, therequired manipulation of the many parts associated with some complexdevices and post-operative movement of the rod-capturing assembliesrelative to the bone anchoring elements due to the weak interfacesbetween the two.

SUMMARY OF THE INVENTION

[0012] In accordance with certain preferred embodiments of the presentinvention, a stabilizing assembly used for stabilizing a spinal columnincludes a fastener having an upper end and a head at the upper end, andat least one anchoring element between the upper and lower ends thereof.The head of the fastener preferably includes a center, an undersideincluding a first radial surface and a top side including a secondradial surface, the first radial surface defining a first radius fromthe center of the head and the second radial surface defining a secondradius from the center of the head, the first radius being greater thanthe second radius. Although the present invention is not limited by anyparticular theory of operation, it is believed that utilizing a fastenerhead having a dual-radius outer surface will provide a stabilizingassembly having a lower overall silhouette, thereby enhancing thecompactness of the assembly. The lower silhouette results, in part, fromthe lower height of the second radial surface at the top of the head.

[0013] The pedicle screw assembly also preferably includes a couplingelement that couples together the fastener and a stabilizing rodinserted into the coupling element. The coupling element desirablyincludes an upper end and a lower end, a rod receiving opening adaptedto receive a stabilizing rod, a bore extending through the lower end ofthe coupling element for receiving the fastener, and a seat adjacent thelower end of the coupling element adapted to engage the first radialsurface of the head when the fastener is positioned in the bore. Incertain preferred embodiments the seat is a conical-shaped seat havingside walls that taper inwardly toward the lower end of the couplingelement. In certain preferred embodiments, the rod-receiving openingbegins at the upper end of the coupling element and extends toward thelower end of the coupling element, the lower end of the rod-receivingopening preferably terminating at U-shaped channels on opposite sides ofthe coupling element.

[0014] The stabilizing assembly also preferably includes a lockingelement associated with the coupling element, the locking element beingadapted to apply a force upon a stabilizing rod positioned in the rodreceiving opening, whereby the stabilizing rod in turn applies a forceupon the second radial surface of the head for forcing the first radialsurface of the head against the conical-shaped seat for preventingfurther pivotal and rotational movement of the fastener and the couplingelement relative to one another. The locking element may include a setscrew having external threads for threadably engaging internal threadsof the coupling element. However, in other embodiments, the couplingelement preferably includes external threads formed on an exteriorsurface of the coupling element and the locking element includes a nuthaving internal threads threadable onto the external threads of thecoupling element.

[0015] In certain preferred embodiments, the fastener is a screwfastener having a longitudinal axis extending between the upper andlower ends thereof, and includes a screwhead having at least one grooveextending from the top surface of the screwhead toward the underside ofthe screwhead, the at least one groove being adapted to receive a driverfor inserting the fastener into bone. The at least one groove preferablyextends in a direction substantially parallel to the longitudinal axisof the fastener. Moreover, the at least one groove desirably includes aplurality of grooves that are equally spaced apart from one anotherabout the head. The fastener also preferably includes a neck portionhaving a reduced diameter for facilitating pivotal movement of thecoupling element and the fastener relative to one another. The neck ofthe fastener may also have a concave surface so as to broaden thepivotal range of the fastener relative to the coupling element.

[0016] The fastener may be inserted into bone using a driver including ashaft having a lower end and a plurality of prongs extending from thelower end of the shaft. The prongs are preferably adapted for beinginserted into the grooves of the head. The shaft of the driver mayinclude external threads that adapted for engaging the internal threadsof the coupling element.

[0017] In operation, the coupling element is anchored in place byanchoring the screw fastener into bone, such as vertebral bone. A pilothole may be formed in the bone before the fastener is anchored to thebone. After the coupling element is anchored in place, a gap preferablyremains between the lower end of the coupling element and the bone sothat the coupling element is free to pivot and rotate relative to thefastener and bone. This pivoting and rotary action facilitates thepositioning of an orthopedic stabilizing rod within the rod-receivingopening of the coupling element.

[0018] After a stabilizing rod has been positioned in the rod-receivingopening of the coupling element, the locking element, i.e., anexternally threaded set screw, is threaded into the internal threads ofthe coupling element. As the set screw is tightened, the underside ofthe set screw abuts the orthopedic rod to apply a downward force throughthe rod onto the second radial surface of the head. As used herein, theterm “downward force” means a force directed toward the lower end of thecoupling element. The downward force applied to the second radialsurface of the head forces the first radial surface of the head into theconical-shaped seat of the coupling element. Engagement of the firstradial surface of the screwhead with the conical-shaped seat locks thecoupling element relative to the screwhead, thereby preventing furtherpivotal and rotary movement of the coupling element. As a result, thelikelihood of post-operative shifting and/or movement of a spine rod orcoupling element relative to one or more of the bone fasteners issignificantly reduced. Thus, the present invention provides for a morereliable spinal fixation device and overcomes the post-operativeshifting problems seen in prior art devices. Moreover, the pedicle screwassembly of the present invention has fewer parts. As a result,implantation operations are greatly simplified and the possibility of acomponent being dropped inside a patient's body greatly reduced.

[0019] In certain preferred embodiments, the fastener may have one ormore holes therein for receiving bone graft material as disclosed inU.S. Pat. No. 4,484,570 to Sutter. Instead of using a screw for securingthe screw to bone, in other preferred embodiments the fastener mayinclude a hook-shaped anchoring element as disclosed in theabove-mentioned U.S. Pat. No. 5,476,464 to Metz-Stavenhagen. Thefastener may also be a structure having barbs on an outer surfacethereof, whereby the fastener is forced into bone and the barbs preventthe fastener from being withdrawn from the bone.

[0020] In certain preferred embodiments, the top surface of the fastenerhead may include a socket adapted to receive a driver, such as ascrewdriver or a hexagonal wrench. In this embodiment, the fastener isattached to bone by inserting the driver into the socket, and thenturning the driver to rotate the fastener in either a clockwise orcounterclockwise direction.

[0021] The coupling element may also have one or more impressions orgrooves formed therein for receiving a controlling device, such as apersuader instrument for seating the rod in the coupling element. Insome embodiments, the impressions or grooves generally extend in adirection substantially perpendicular to the longitudinal axis of thecoupling element. The groove or blind holes may be formed in theexterior surface of the coupling element.

[0022] The interior surface of the coupling element at the lower endthereof preferably defines the seat adapted for engaging the firstradial surface at the underside of the head and for allowing the head topivot relative to the coupling element before being locked in place. Theseat is preferably provided adjacent the lower end of the couplingelement. The seat may define a conical shape or a convex shape. Inparticular preferred embodiments, the seat is a conical-shaped seat. Thewalls of the conical-shaped seat preferably taper inwardly toward oneanother so that the diameter of the walls at the lower end thereof isless than the outer diameter of the head.

[0023] During assembly of the above-mentioned stabilizing device, aportion of the fastener is passed through the bore of the couplingelement until the underside of head is positioned adjacent theconical-shaped seat of the coupling element. During a spinal fixationoperation, after the fastener has been anchored in bone, the couplingelement remains free to pivot relative to the fastener. Moreover, a gappreferably exists between the bottom of the coupling element and bone,the presence of the gap facilitating pivoting movement of the couplingelement. The neck portion of the fastener, preferably having a concavesurface with a diameter less than the diameter of the threaded portionof the fastener, enables the coupling element to pivot through a broaderrange of angles relative to the fastener. Thus, a spine rod may be moreeasily positioned within the rod receiving opening of the couplingelement. After the rod has been positioned within the rod receivingopening, a locking element is threaded into the threads of the couplingelement. As the locking element tightens down upon the rod, the rod, inturn, exerts a downward force onto the second radial surface of thehead. The downward force applied to the second radial surface of thehead forces the first radial surface of the head into the conical-shapedseat of the coupling element. Engagement of the first radial surface ofthe head with the conical-shaped seat locks the coupling elementrelative to the head, thereby preventing further pivotal and rotarymovement of the coupling element. As a result, the likelihood ofpost-operative shifting and/or moving of the pedicle screw assembly isgreatly reduced, thereby minimizing the occurrence of post-operativecomplications for spinal implant patients.

[0024] The present invention also preferably includes a tool forsecuring or anchoring the fastener in bone. The tool is preferably adriver having a rotatable shaft and one or more prongs extending from anend of the shaft for engaging grooves in the head. In preferredembodiments, the driver has one prong for each groove in the head of thefastener. The driver may also have external threads at a lower end ofthe shaft. The external threads are preferably adapted for engaging theinternal threads of the coupling element when a fastener is beinganchored to the bone. The engagement of the external threads of thedriver and the internal threads of the coupling element generallystabilizes the assembly when the fastener is secured to bone.Specifically, the engagement of the threads prevents the couplingelement from moving relative to the fastener when driving the fastenerinto bone, thereby simplifying installation of the fasteners.

[0025] These and other objects, features and advantages of the presentinvention will be more readily apparent from the detailed description ofpreferred embodiments set forth below, taken in conjunction with theaccompanying drawings.

[0026] In other preferred embodiments, a coupling element for astabilizing assembly desirably includes an upper end and a lower end, arod receiving opening adapted to receive a stabilizing rod, a boreextending through the lower end of the coupling element for receiving afastener having a head with a first radial surface of a first diameter,and a seat adjacent the lower end of the coupling element adapted toengage an underside of the head of the fastener. The coupling elementpreferably includes threads extending from the upper end toward thelower end of the coupling element, and an annular lip between thethreads and the seat of the coupling element, whereby the annular liphas a second diameter that is less than the first diameter of the firstradial surface of the head.

[0027] In still other preferred embodiments, a coupling element for astabilizing assembly includes an upper end and a lower end remotetherefrom, and a rod receiving opening adapted to receive a stabilizingrod. The coupling element preferably ahs an exterior surface and aninterior surface defining a central bore extending through the lower endof the coupling element. A seat adjacent the lower end of the couplingelement is desirably adapted to engage an underside of a head of thefastener, whereby the coupling element includes one or more cuts betweenthe rod-receiving opening and the exterior surface thereof forminimizing the width of the coupling element. Although the presentinvention is not limited by any particular theory of operation, it isbelieved that providing cuts at the edge of the rod receiving openingreduces the width of the coupling element so that more coupling elementsmay be fit onto a given length of a stabilizing rod. The cuts alsominimize the sharp edges on the coupling element, thereby reducing thechance that the coupling element will irritate a patient's tissue and/orcutting a surgeon's glove.

[0028] These and other objects, features and advantages of the presentinvention will be more readily apparent from the detailed description ofpreferred embodiments set forth below, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 shows a front elevation view of a fastener for astabilizing assembly, in accordance with certain preferred embodimentsof the present invention

[0030]FIG. 2 shows a plan view of the fastener shown in FIG. 1.

[0031]FIG. 3A shows a fragmentary, cross-sectional view of the fastenershown in FIG. 2 taken along line IIIA-IIIA of FIG. 2.

[0032]FIG. 3B shows an expanded view of a portion of the fastener shownin FIG. 3A.

[0033]FIG. 4 shows a perspective view of a coupling element for astabilizing assembly, in accordance with certain preferred embodimentsof the present invention.

[0034]FIG. 5 shows a fragmentary, cross-sectional view of the couplingelement shown in FIG. 4.

[0035]FIGS. 6A and 6B show a method of assembling the fastener of FIGS.1-3B with the coupling element of FIGS. 4-5, in accordance with certainpreferred embodiments of the present invention.

[0036]FIG. 7 shows a perspective view of the assembly shown in FIG. 6B.

[0037]FIG. 8 shows a perspective view of a driver for engaging theassembly of FIG. 7 for driving the fastener into bone, in accordancewith certain preferred embodiments of the present invention.

[0038]FIG. 9A shows the assembly of FIG. 7 after the fastener has beenanchored in bone.

[0039]FIG. 9B shows an expanded view of a portion of FIG. 9A with thecoupling element being pivoted to receive a stabilizing rod.

[0040]FIG. 9C shows a stabilizing rod secured to coupling element by aset screw, in accordance with certain preferred embodiments of thepresent invention.

[0041]FIG. 10 shows a cross-sectional view of a coupling element, inaccordance with further preferred embodiments of the present invention.

[0042]FIG. 11 shows a fragmentary view of the coupling element shown inFIG. 10.

[0043]FIG. 12 shows a fragmentary view of a fastener, in accordance withcertain preferred embodiments of the present invention.

[0044]FIGS. 13A and 13B show a method of assembling the fastener to acoupling element, in accordance with certain preferred embodiments ofthe present.

[0045]FIG. 14 shows a perspective view of a coupling element, inaccordance with further preferred embodiments of the present invention.

[0046]FIG. 15 shows a front elevation view of the coupling element ofFIG. 14.

[0047]FIG. 16 shows a plan view of the coupling element shown in FIGS.14 and 15.

[0048]FIG. 17 shows a front elevation view of a screw fastener coupledwith a coupling element, in accordance with further preferredembodiments of the present invention.

[0049]FIG. 18 shows a fastener for a stabilizing assembly in accordancewith further preferred embodiments of the present invention.

[0050]FIG. 19 shows a coupling element having external screw threads inaccordance with another preferred embodiment of the present invention.

DETAILED DESCRIPTION

[0051] Referring to FIG. 1, in accordance with certain preferredembodiments of the present invention, a pedicle screw assembly includesa fastener 20, such as a screw fastener having a tip end 22 forinsertion into bone and a head 24 at an upper end thereof. The screwfastener 20 preferably has external screw threads 26 that extend betweenthe tip end 22 and screwhead 24. The screw threads 26 terminate at aneck 28 preferably located between screwhead 24 and an upper end of thescrew threads 26. The neck 28 desirably has a concave surface having adiameter that is less than the diameter of the screw threads. Thereduced diameter neck 28 allows the screw fastener 20 to pivot androtate through a broader range of motion, as will be described in moredetail below. The screw fastener, including the external threads 26,neck 28 and screwhead 24, are preferably made of a non-organic materialthat is durable and that can be implanted in a human body, such astitanium or stainless steel.

[0052] Referring to FIGS. 1 and 2, screwhead 24 preferably has anunderside 30 defining a first radial surface and a top side 32 defininga second radial surface. Screwhead 24 also desirably includes one ormore grooves 34 that extend in a direction substantially parallel to thelongitudinal axis of screw fastener 24. Referring to FIG. 2, in onepreferred embodiment, screwhead 24 includes a plurality of grooves 34evenly spaced from one another and extending around the outer perimeterof screwhead 24. The top surface 32 screwhead 24 is preferably centeredon the plurality of grooves 34.

[0053] Referring to FIGS. 3A and 3B, screwhead 24 includes a center 36,whereby the underside 30 of screwhead 24 defines the first radialsurface having a radius R₁ from center 36. Screwhead 24 includes topsurface 32 having second radial surface at a second radius R₂ fromcenter 36. The plurality of grooves 34 are preferably adapted to receiveprongs of a driver used to screw the screw fastener into bone, as willbe described in more detail below.

[0054] Referring to FIGS. 4 and 5, pedicle screw assembly also includesa coupling element 40 for coupling an orthopedic stabilizing rod withthe screw fastener shown in FIGS. 1-3B. Coupling element 40 ispreferably made of an inert material such as titanium or stainlesssteel. Coupling element 40 has an upper end 42, a lower end 44, and alongitudinal axis C-C extending between the upper and lower ends.Coupling element 40 also preferably has an outer surface 46 including aconvex surface at the lower end 44 thereof and a cylindrical surface atthe upper end thereof. Outer surface 46 also preferably includes one ormore grooves 48 formed therein so that coupling element 40 may begrasped and/or maneuvered using a securing element or tool, such as apersuader instrument used to seat the orthopedic rod in the pediclescrew assembly. The grooves 48 preferably extend in directionssubstantially perpendicular to the longitudinal axis C-C of couplingelement 40.

[0055] The coupling element 40 has a bore 50 for receiving the screwfastener the bore extending along the longitudinal axis C-C of couplingelement 40. The bore 50 defines an inner surface of coupling element 40and has internal threads 44 extending from the upper end 42 of thecoupling element toward a cavity 52 adjacent lower end 44. The lower endof cavity 52 preferably has a conical shaped seat 54 including sidewallstapering inwardly toward the lower end 44. In other embodiments, thethreads on the coupling element may be external threads.

[0056]FIGS. 6A and 6B show one preferred method for assembling screwfastener 20 with coupling element 40. Referring to FIG. 6A, tip end 22of screw fastener 20 is passed through bore 50 of coupling element 40from the upper end 42 toward the lower end 44 of the coupling element sothat the threaded portion of screw fastener passes through bore 50. Thethreaded portion 26 of screw fastener 20 is able to pass freely throughbore 50 because the threaded portion 26 has an outer diameter that isless than the internal diameter of the internal threads 44 of couplingelement 40. Referring to FIG. 6B, screw fastener 20 continues to beinserted toward the lower end of coupling element 40 until screwhead 24is disposed within cavity 52 of coupling element 40 and the underside ofscrewhead engages the seat of coupling element.

[0057] Referring to FIG. 7, after the screw fastener 20 has beenassembled with coupling element 40, the neck 28 of screw fastener 20 isfree to pivot and rotate relative to coupling element. As mentionedabove, neck 28 preferably has a reduced diameter and may also have aconcave outer surface so that the screw fastener 20 and coupling elementmay pivot relative to one another over a broader range of angles.

[0058] After screw fastener 20 and coupling element have been assembledtogether, the subassembly is ready to be inserted into bone 60. In afirst step, the screw fastener 20 may be anchored to bone 60 by drillinga pilot hole into the bone. The tip end (not shown) of screw fastener 20may then be placed in the pilot hole and the screw fastener screwed intobone 60 using a driver or tool. One preferred driver 62 for drivingscrew fastener 20 into bone 60 includes a rotatable shaft 64 having alower end 66 with a plurality of downwardly extending prongs 68. Theprongs 68 are sized for fitting into the grooves 34 of the screwhead(not shown) of screw fastener 20. Upon rotation of shaft 64, prongs 68engage grooves 34 of screw fastener 20 for rotating screw fastener 20and screwing the fastener into bone 60. Driver 62 may also includeexternal threads 70, preferably between shaft 64 and prongs 68. Externalthreads 70 are designed for threadably mating with the internal threads44 of coupling element 40 (FIGS. 4-5). The mating engagement of theexternal threads 70 of driver 62 and the internal threads 44 of couplingelement 40 generally stabilizes the pedicle screw assembly when drivingthe screw fastener 20 into bone 60.

[0059] Referring to FIGS. 9A and 9B, after screw fastener 20 is anchoredin bone 60, coupling element 40 remains free to pivot and rotaterelative to the screw fastener so that an orthopedic stabilizing rod 72may be positioned within the rod receiving opening 74 of couplingelement 40. Rod receiving opening 74 preferably includes a U-shapedopening extending from the top 42 of coupling element 40. Moreover,after screw fastener has been fully inserted into bone, a gap existsbetween the lower end 44 of coupling element 40 and bone 60. The gapfacilitates pivotal and rotational movement of coupling element 40relative to screw fastener 20. The coupling element 40 may then be moved(e.g. pivoted) by engaging grooves 48 with a tool or by grasping theouter body portion of the coupling element. Coupling element 40 wouldthen be pivoted and/or rotated so that an orthopedic rod 72 can bepositioned in the rod receiving opening 74, as shown in FIG. 9B.

[0060] Referring to FIG. 9C, after stabilizing rod 72 has beenpositioned within coupling element 40, a set screw 76 having externalthreads (not shown) is screwed into the internal threads 44 of couplingelement 40. Set screw 76 continues to be threaded into the internalthreads 44 until an underside 78 of set screw 76 abuts againststabilizing rod 72. Set screw 76 is then further rotated into internalthreads 44 for locking stabilizing rod 72 in rod receiving channel 74.The tightened set screw 76 applies a downward force through rod 72 ontothe second radial surface at the top side 32 of screwhead 24. Thedownward force applied to the second radial surface of screwhead 24forces the first radial surface at the underside 30 of screwhead 24 intothe conical-shaped seat 54 of coupling element 40. Engagement of thefirst radial surface at the underside 30 of screwhead 24 with theconical-shaped seat 54 creates a spherical surface/conical surfacefriction lock that locks the coupling element 40 relative to thescrewhead 24, thereby preventing further pivotal and rotary movement ofcoupling element 40 and screw fastener 20 relative to one another.Although the present invention is not limited by any particular theoryof operation, it is believed that the engagement of the sphericalsurface of the screwhead with the conical seat of the coupling elementdramatically improves the locking force exerted at the interface of thescrewhead and the coupling element.

[0061] Referring to FIG. 10, in accordance with other preferredembodiments of the present invention, a coupling element 140 for astabilizing assembly includes an upper end 142 and a lower end 144.Coupling element 140 also includes an outer surface 146 extendingbetween upper and lower ends 142, 144, the outer surface 146 includingone or more grooves 148. Coupling element also includes a centrallylocated bore 150 extending between the upper end 142 and lower end 144along longitudinal axis C-C. Bore 150 is surrounded by interior threads151 extending from the upper end 142 toward the lower end 144. Couplingelement 140 also includes a cavity 152 adjacent lower end 144, thecavity including a conical-shaped seat 154 having sidewalls that taperinwardly toward the lower end 144 of coupling element 140. Couplingelement 140 also preferably includes an interior wall 153 havingdiameter D_(W) between interior threads 151 and cavity 152, and a lip155 between interior wall 153 and cavity 152. The lip 155 has a diameterD_(L) that is less than the diameter D_(W) of interior wall 153. Asshown in FIG. 12, the outer diameter D_(S) of the first radial surface130 of screwhead 124 is greater than the diameter D_(L) of the lip 155of coupling element. As a result, lip 155 serves as a detent that holdsfastener 120 in the cavity 152 of coupling element 140 after thescrewhead of fastener 120 has been assembled with the coupling element140.

[0062]FIG. 11 shows a magnified view of a portion of the couplingelement 140 shown in FIG. 10. As described above, coupling element 140includes bore 150 extending from an upper end (not shown) toward lowerend 144 thereof, and an interior wall 153 extending between internalthreads 151 and cavity 152. Cavity 152 includes conical-shaped seat 154having inwardly tapering sidewalls 154. Coupling element 140 includeslip 155 positioned between interior wall 153 and cavity 152. Lip 155 hasa diameter D_(L) that is less than the diameter D_(W) of the interiorwall 153 of coupling element 140.

[0063]FIG. 12 shows screw fastener 120 having screwhead 124 at an upperend thereof, the screwhead including a first radial surface 130 at anunderside thereof and a second radial surface 132 at a top side ofscrewhead 124. Screwhead 124 includes a center 136, a first radialsurface 130 from center 136 having has a radius R₁ and a second radialsurface 132 from center 136 having a second radius R₂, whereby R₁ isgreater than R₂. The first radial surface of screwhead 124 defines anouter diameter D_(S) that is two times the length of R₁.

[0064]FIGS. 13A and 13B show screw fastener 120 being assembled with thecoupling element 140 shown in FIGS. 10 and 11. As mentioned above,coupling element 140 includes lip 155 having a diameter D_(L) that isless than the diameter D_(S) of the first radial surface 130 ofscrewhead 124, however, the outer diameter D_(S) of the first radialsurface 130 of screwhead 124 is less than the inner diameter of innerwall 153.

[0065] Referring to FIGS. 13A and 13B, during assembly of screw fastener120 to coupling element 140, the screw fastener 120 is passed throughbore 150 so that screw threads 126 pass through the opening at lower end144 of coupling element 140. Because the outer diameter D_(S) ofscrewhead 124 is less than the inner diameter of inner wall 153,screwhead 124 passes easily through bore 150 until first radial surface130 engages lip 155. Because the inner diameter D_(L) of lip 155 is lessthan the outer diameter D_(S) of the first radial surface 130 ofscrewhead 124, the lip 155 acts as a detent and the screwhead must beforced through the reduced diameter of lip 155. Referring to FIG. 13B,after the outer diameter D_(S) of screwhead 124 has passed by lip 155,the screwhead is retained within cavity 152 by lip 155, with couplingelement 140 pivotable relative to screwhead 124 for capturing astabilizing rod. After stabilizing rod is captured within the U-shapedopening of coupling element 140, a set screw (not shown) may be threadedinto internal threads 151 of coupling element 140 for capturing thestabilizing rod within the U-shaped opening. The set screw is thenpreferably tightened for exerting a downward force upon the stabilizingrod which, in turn, applies a force to the second radial surface 132 ofscrewhead 124. The downward force on the second radial surface 132forces the first radial surface 130 into the conical-shaped seat ofcoupling element for locking the screwhead and coupling element relativeto one another.

[0066] FIGS. 14-16 show a coupling element 240 in accordance withfurther preferred embodiments of the present invention. Coupling element240 includes upper end 242, lower end 244 and outer wall 246 extendingbetween upper and lower ends 242, 244. The outer surface 246 of couplingelement 240 includes grooves 248 on opposing arms thereof. Couplingelement 240 has central bore 150 extending between upper and lower endsthereof. Coupling element 240 has a first arm 261A and a second arm 261Bon either side of U-shaped rod-receiving opening 174, the U-shapedrod-receiving opening being adapted to receive a stabilizing rod (notshown). The edges of the U-shaped opening include cuts 263 formedtherein. The cuts 263 reduce the profile or width of the couplingelement, thereby minimizing interference with other coupling elementswhen a series of coupling elements are connected with a stabilizing rod.The cuts 263 allow the coupling elements 240 to be packed more tightlytogether and to be secured over each vertebrae, thereby improving fusionof a spinal segment. Although the present invention is not limited byany particular theory of operation, it has been observed that somepatients have relatively small vertebrae, making it difficult to securea coupling element over each vertebrae. As a result, some of thevertebrae may not have a section of the stabilizing assembly attachedthereto, a situation that may adversely affect stabilization and fusionof a spine segment because the entire portion of the spine segment isnot being stabilized. In addition, the cuts 263 minimize the occurrenceof sharp edges on the coupling element that may irritate a patient'stissue or cut through a surgeon's surgical glove.

[0067]FIG. 17 shows a front elevation view of the coupling element 240of FIGS. 14-16 assembled with screw fastener 220. Coupling element 240includes internal threads 9not shown) for receiving set screw 276.Coupling element 240 includes cuts 263 for minimizing the profile of thecoupling element and reducing the occurrence of sharp edges.

[0068]FIG. 18 shows a fastener 320 in accordance with another embodimentof the present invention. Fastener 320 includes head 324 having a firstradial surface 330 having radius R₁ from center 336 and second radialsurface 332 having radius R₂ from center 336. The first radius R₁, isgreater than the second radius R₂Fastener 320 includes hook 370 forsecuring the fastener to bond (not shown).

[0069]FIG. 19 shows an assembly in accordance with another embodiment ofthe present invention including a coupling element 440 having externalthreads 444 extending from an upper end thereof. The assembly alsoincludes a locking element 476 having internal threads 477 adapted tothread onto the external threads 444 of coupling element 440.

[0070] Although the invention herein has been described with referenceto particular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A method for stabilizing a spine comprising: providing a couplingelement having upper and lower ends, a rod receiving opening adapted toreceive an elongated stabilizing rod, a bore extending through the lowerend and a conical-shaped seat surrounding said bore adjacent the lowerend; providing a fastener having upper and lower ends, a head having aradial surface, and at least one anchoring element between the lower endof said fastener and the head; assembling said fastener with saidcoupling element so that the lower end of said fastener passes throughthe bore of said coupling element and the radial surface of said headengages the conical-shaped seat; anchoring said fastener to bone; movingsaid coupling element relative to said fastener for capturing saidelongated stabilizing rod in the rod receiving opening; urging saidcaptured stabilizing rod toward the head of said fastener so that saidrod contacts said head and forces the radial surface of said headagainst the conical-shaped seat of said coupling element for lockingsaid coupling element from further movement relative to said fastener.2. The method as claimed in claim 1, wherein the urging step comprises:providing a locking element associated with said coupling element; usingsaid locking element in cooperation with said coupling element to applya force upon said stabilizing rod positioned in said rod receivingopening.
 3. The method as claimed in claim 2, wherein said couplingelement has threads extending from the upper end thereof toward thelower end thereof and said locking element has threads adapted formating with the threads of said coupling element during the urging step.4. The method as claimed in claim 3, wherein said coupling element hasinternal threads formed on an interior surface thereof and said lockingelement has external threads.
 5. The method as claimed in claim 3,wherein said coupling element has external threads formed on an externalsurface thereof and said locking element has internal threads.
 6. Themethod as claimed in claim 1, wherein said coupling element and saidfastener are made from a material selected from the group consisting oftitanium and stainless steel.
 7. The method as claimed in claim 1,wherein said fastener is a screw fastener and the at least one anchoringelement comprises screw threads extending between the upper and lowerends thereof.
 8. The method as claimed in claim 1, wherein the at leastone anchoring element comprises a hook at the lower end of saidfastener.
 9. A method of stabilizing a spinal column comprising:providing a fastener including a bone anchoring element and a headhaving a first radial surface with a first radius at an undersidethereof and a second radial surface with a second radius at a top sidethereof, wherein the first radius at the underside is greater than thesecond radius at the top side; providing a coupling element having upperand lower ends, a rod receiving opening adapted to receive an elongatedrod, a bore extending through the lower end of said coupling element,and a conical-shaped seat; assembling said fastener with said couplingelement so that said fastener passes through said bore with the firstradial surface at the underside of said head opposing the conical-shapedseat; anchoring said fastener to bone; after the anchoring step, movingsaid coupling element for capturing said elongated rod in the rodreceiving opening; urging said elongated rod against said head of saidfastener for forcing the first radial surface of said head against theconical-shaped seat of said coupling element for locking said couplingelement from further movement relative to said fastener.
 10. The methodas claimed in claim 9, wherein said coupling element includes anexterior surface having one or more notches formed therein, and whereinthe moving step includes engaging said notches with a gripping tool. 11.The method as claimed in claim 9, wherein the urging step includes usinga locking element in association with said coupling element for forcingsaid stabilizing rod against the second radial surface of said headwhich in turn forces the first radial surface of said head against theconical-shaped seat of said coupling element for preventing saidcoupling element and said fastener from pivoting and rotating relativeto one another.
 12. The method as claimed in claim 9, wherein saidfastener includes screw threads extending between upper and lower endsthereof.
 13. The method as claimed in claim 9, wherein said fastenerincludes a hook.
 14. A method of stabilizing a vertebral columncomprising: providing a coupling element having upper and lower ends, arod receiving opening adapted for receiving an elongated stabilizingrod, an exterior surface, an interior surface defining a central boreextending through the lower end thereof, and a conical-shaped seatadjacent the lower end; providing a fastener having upper and lowerends, at least one anchoring element between the upper and lower ends,and a head at the upper end having a radial surface and assembling saidfastener with said coupling element so that the radial surface of saidhead engages the conical-shaped seat and the lower end of said fastenerpasses through said central bore; anchoring the lower end of saidfastener to vertebral bone; after the anchoring step, moving saidcoupling element to capture said stabilizing rod in the rod receivingopening; utilizing a locking element in association with said couplingelement to urge said stabilizing rod into direct engagement with thehead of said fastener for forcing the radial surface of said headagainst the conical-shaped seat of said coupling element for preventingfurther movement of said coupling element and said fastener relative toone another.
 15. The method as claimed in claim 14, wherein saidfastener is a screw fastener and said anchoring element comprises screwthreads.
 16. The method as claimed in claim 14, wherein said couplingelement and said fastener are made of materials selected from the groupconsisting of titanium and stainless steel.
 17. The method as claimed inclaim 15, wherein said coupling element has threads extending from theupper end toward the lower end thereof and said locking element hasthreads adapted for meshing with the threads of said coupling element.18. The method as claimed in claim 14, wherein the head of said fastenerincludes at least one groove extending from the top surface toward theunderside thereof, said at least one groove being adapted for receivinga driver for inserting said fastener into bone.
 19. The method asclaimed in claim 18, wherein said at least one groove includes aplurality of grooves spaced apart from one another.
 20. The method asclaimed in claim 19, wherein the anchoring step comprises: providing adriver having a shaft with a lower end and a plurality of prongsextending from the lower end; inserting the prongs into the grooves ofsaid head; rotating said driver for driving said fastener into thevertebral bone.